1. Field of the Invention
The invention generally relates to electronic circuits for processing voltages that may be used in units or subunits of communication systems such as WLAN (Wireless Local Area Network) systems.
2. Description of the Related Art
A wireless local area network is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN. Using radio frequency (RF) or infrared technology, WLAN systems transmit and receive data over the air, minimizing the need for wired connections. Thus, WLAN systems combine data connectivity with user mobility. Most WLAN systems use spread spectrum technology, a wide-band radio frequency technique developed for use in reliable and secure communication systems. The spread spectrum technology is designed to trade-off bandwidth efficiency for reliability, integrity and security.
One element in wireless communication systems are RF transceivers. Today, RF transceivers are often provided as integrated circuits and the realization of RF transceivers in highly integrated circuits may be a requirement for applications such as those in wireless local area networks and in the cellular telephony to achieve very high dynamic range and very high frequency on the one hand and a low power consumption and a reduction in the passive components on the other hand.
One possibility to satisfy these requirements may be to build RF transceivers in CMOS (Complementary Metal Oxide Semiconductor) technology. The CMOS technology may offer low power consumption and a high level of integration.
The central device in such technologies is the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistor. It is a three or four terminal device that draws no power from an input signal and allows for very fast switching. The fourth terminal is connected to the substrate and is called the bulk.
FIG. 1 shows a typical electronic circuit that may act as an absolute value generator and comprises a current source 100 and two p-channel MOSFET transistors 110, 140. The current source 100 is connected to the source terminals of the p-channel MOSFET transistors for supplying the current to the transistors. Further, the source terminal of each transistor is connected to its bulk terminal. The electronic circuit of FIG. 1 further comprises two input terminals 120, 130 wherein one is connected to the gate of the first transistor 110 and the other is connected to the gate of the second transistor 140 to provide respective input voltages. The drain terminals of the transistors 110, 140 are connected to a ground line to provide a common ground level. An output terminal 150 is provided at a point connecting the current source 100 with the source terminals of the transistors 110, 140. It can further be seen that the transistors 110, 140 are connected in parallel to each other.
The shown electronic circuit of FIG. 1 is disadvantageously affected by a poor accuracy in particular if small voltages, i.e., Vpeak<Vgs−Vthr and large voltages, i.e., Vpeak>(Vgs−Vthr)*1.414 are processed. When for instance a large signal is delivered to one of the two input terminals 120, 130 and the other input terminal receives a small signal, one transistor turns off (Vgs<Vthr) while the other has to carry twice the current: Vgs≅1.414*Vgs(0V). This situation may results in an additional level shift caused by nonlinear changes of a gate source voltage and may undesirably change the value of the voltage of the output terminal 150.
Therefore, the conventional electronic circuits do often not meet the requirements of accuracy, operating speed and precision.